Thor
Captain America
Hulk
Ironman
The movie will once again center around them. All other new avengers will be supporting characters, in the sense that Fury was or black widow was
Given that, the next characters are are going to get
Ant-man
Vision
I am not feeling wasp becoming an avenger. Not sure why, just don't see it happening.

Avengers 3
We will have the addition of Ms Marvel, if the Kree are introduced, and Black Panther